Been driving long distances lately as part of the job hunt, and I've noticed an issue in my '66 130.

The car starts just fine, runs great for about the first 90 minutes of a long trip. Then for whatever reason, the car starts behaving as though there isn't enough gas in the mixture. Bits of surging here and there.

Pulling over and increasing the fuel mixture + idle helps a bit, but it doesn't make the surging go completely away.

The driving is standard freeway fare. 60-70 mph or so (with the car in Overdrive the whole time).

Also, when I make a stop and jump right back in the car, I find I actually need to use the choke to get it to fire, and then I have to keep the choke out for a minute or so to keep the idle up (other wise it flirts with stalling.)

Once the car cools down, all is normal.

What is happening after 90 minutes that's causing this to happen? Any ideas what the cause is? I'm pretty sure it's a carb issue, but I'm not sure where to begin. The car has SUs.

Thanks as always.
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